Electrochemical Preparation of a Carbon/Cr-O-C Bilayer Film on Stainless Steel in Molten LiCl-KCl-K2CO3

A carbon film was electrochemically deposited on 304 stainless steel by reduction of carbonate ions in molten LiCl-KCl-K2CO3. A Cr-O-C interlayer was prepared by a joint process of thermal exposure of the steel in air and subsequent electrochemical reactions in molten salt for the enhancement of adhesion between the carbon film and the substrate. The bilayer film was delaminated gradually using electrochemical polarization in an aqueous NaCl solution, and was characterized by XRD, SEM, and XPS. Chromium element aggregates in the oxide scale from the 304 stainless steel substrate during the oxidation process, and transforms to chromium oxycarbide during electro-deoxidation of the oxide scale and diffusion of carbon nucleated from electro-reduction of carbonate ions. The interlayer mainly presents the CrO1.13C0.12 phase, which contains Cr-C and Cr-O bonds confirmed by XPS analysis. The presence of the CrO1.13C0.12 interlayer is an important factor for a continuous and adhesive carbon film on 304 stainless steel. (C) 2014 The Electrochemical Society. All rights reserved.